Systems for corona discharge surface treatment are known. Some prior art systems are disclosed in U.S. Pat. Nos. 4,556,795, 4,564,759, and 4,636,640. The systems disclosed in each of those patents has at least two opposed electrodes, one of which is a rotating roll, which moves a material to be treated (commonly in the form of a continuous web of film-like material) during its treatment. The rotating roll electrode may or may not have an insulating covering, called a "buffer dielectric," on its surface. The rotating roll electrode is most often opposed by a plurality of fixed electrodes that are adjustable relative to the rotating roller so as to establish a predetermined treatment gap therebetween through which the film being treated is moved.
The rotating roll and the fixed electrodes typically have a high AC voltage applied across them which creates a high voltage electrostatic field. Normally, the rotating roll electrode is grounded, with the fixed electrodes being connected to the high voltage side of the power supply. The high voltage field establishes a corona discharge between the electrodes. The surface of the film interposed between the rotating and fixed electrodes is thus subjected to the corona discharge. The corona discharge treatment results in the molecules on the surface of the film being modified so as to increase the wettability of the film which, in turn, makes the surface more amenable to receiving and retaining an applied coating, such as for example printing ink for printing indicia on the film.
There are primarily two types of fixed electrodes used in corona discharge treatment of film materials. These types are commonly referred to as "bare roll" electrodes and "conventional" electrodes. Conventional electrodes are usually used when the rotating roll electrode has its outer surface covered by the buffer dielectric. Conventional electrodes used in conjunction with an insulated roll electrode can corona discharge treat only non-conductive materials such as paper or plastic. In a bare roll system, the rotating roll electrode usually is not covered by a buffer dielectric (hence the term "bare"). Instead, in a bare roll system, the buffer dielectric is on the fixed electrode. A bare roll system is always used when conductive materials, such as metallized materials or foils, are to be corona discharge treated. While a bare roll system can also be used to treat non-conductive materials, it has inherent inefficiencies which make it a poor choice for treating some non-conductive materials.
In practice, it is often desired to change a corona discharge treating system for a "bare roll" system to a "conventional" system, or vice versa. This typically consumes an inordinate amount of time to remove one type of electrodes and then install and align the other type of electrodes. This includes production line down time, as well as personnel time. When changing from one system to the other, one type of fixed electrode must first be disconnected and removed, and then the other type of fixed electrode installed. After installation, the spacing between the fixed electrodes and rotating electrode must be checked and sometimes adjusted so as to provide proper clearance between the rotating roll and fixed electrodes. It is desirable to avoid inordinate production line down time and set up time.
Moreover, materials to be treated often have different widths that should be taken into account in order to provide for proper corona discharge treatment. For example, for proper treatment it is desired that the available energy from the high voltage power source be applied across the full width of the material being treated. As the width of the material is increased or decreased, the number of fixed electrodes across the width of the material must be correspondingly increased or decreased. It is desired to easily accommodate different widths of materials being treated.
Accordingly, it is one object of the present invention to provide means for easily accommodating different widths of materials that receive corona discharge treatment.
It is a further object of the present invention to provide means that accommodate separate electrodes, such as conventional and bare-roll electrodes, respectively, which do not require the disconnection or reconnection typically required for separate electrodes.
Another object of the present invention is to provide a corona discharge surface treating system having electrodes that are easily reconfigured so as to run either "bare roll" or "conventional" treatment processes.
Other objects, advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawings.